The present invention relates to knee prostheses for replacing the articular surfaces of a diseased or injured human knee. More particularly, the present invention relates to a knee prosthesis having an extended range of flexion.
Disease and trauma affecting the articular surfaces of the knee joint are commonly effectively treated by surgically replacing the articulating ends of the femur and tibia with prosthetic femoral and tibial implants, referred to as total knee replacements (TKR). These implants are made of materials that exhibit a low coefficient of friction as they articulate against one another so as to restore normal, pain free, knee function. Modern TKR's are tricompartmental designs. That is, they replace three separate articulating surfaces within the knee joint; namely the patello-femoral joint and the lateral and medial inferior tibio-femoral joints. These implants are designed to articulate from a position of slight hyperextension to approximately 115 to 130 degrees of flexion. Such a tricompartmental design can meet the needs of most TKR patients even though the healthy human knee is capable of a range of motion (ROM) approaching 170 degrees. However, there are some TKR patients who have particular need to obtain very high flexion in their knee joint, usually as a result of cultural considerations. For many in the orient, and for some in the west, a TKR which permits a patient to achieve a ROM in excess of 150 degrees is desirable to allow deep kneeling, squatting, and sitting on the floor with the legs tucked underneath.